Petr Kadlec

Structural and mechanical behaviour of LLDPE/HNT nanocomposite films

The paper briefly describes structural and mechanical influences of Halloysite nanotubes (HNT) in different level of fulfilment (0, 1, 3, 7 wt%) in the LLDPE commonly used in the cable industry. The influence of HNT on the polymer has been observed and evaluated through the average crystallite size and the micro- deformation by X-Ray diffractometry and the imaging of SEM. Despite the certain inter-phase tension between the polymer and HNT, the influence on the mechanical and combustion behaviour was observed. Measurement showed a higher content of agglomerates in the sample with 7 wt% HNT fulfilment.

Dielectric analysis of halloysite nanotubes LLDPE nanocomposite compounds

The aim of this paper is to investigate the influence of HNT on the dielectric properties of LLDPE (linear low density polyethylene) nanocomposite compounds in the different level of fulfillment (0, 1, 3, 7 wt%). The utilization of these HNT/LLDPE nanocomposite compounds can be seen in the cable industry, where the dielectric properties are essential. Used experimental compounds have been prepared in the laboratory blades mixer Brabender W50 EHT and the plasticorder Brabender PLE 651. Immediately after mixing, the molten compounds were removed from the mixer, inserted into the spacer, and pressed into films of 0.25 mm thickness. Dielectric properties in the DC field (polarization current, reading of polarization index, volume resistivity) of the individual samples were measured and the temperature and frequency range by Broadband dielectric spectroscopy Alpha-A (Novocontrol) were investigated. Samples have been subjected to the dielectric strength test according to standards. As results showed, experiment...

Magnesium Oxide Nanoparticles: Dielectric Properties, Surface Functionalization and Improvement of Epoxy-Based Composites Insulating Properties

Composite insulation materials are an inseparable part of numerous electrical devices because of synergy effect between their individual parts. One of the main aims of the presented study is an introduction of the dielectric properties of nanoscale magnesium oxide powder via Broadband Dielectric Spectroscopy (BDS). These unique results present the behavior of relative permittivity and loss factor in frequency and temperature range. Following the current trends in the application of inorganic nanofillers, this article is complemented by the study of dielectric properties (dielectric strength, volume resistivity, dissipation factor and relative permittivity) of epoxy-based composites depending on the filler amount (0, 0.5, 0.75, 1 and 1.25 weight percent). These parameters are the most important for the design and development of the insulation systems. The X-ray diffraction patterns are presented for pure resin and resin with optimal filler amount (1 wt %), which was estimated according to measurement results. Magnesium oxide nanoparticles were also treated by addition of silane coupling agent (γ-Glycidoxypropyltrimethoxysilane), in the case of optimal filler loading (1 wt %) as well. Besides previously mentioned parameters, the effects of surface functionalization have been observed by two unique measurement and evaluation techniques which have never been used for this evaluation, i.e., reduced resorption curves (RRCs) and voltage response method (VR). These methods (developed in our departments), extend the possibilities of measurement of composite dielectric responses related to DC voltage application, allow the facile comparability of different materials and could be used for dispersion level evaluation. This fact has been confirmed by X-ray diffraction analyses.

Complex analysis of novel insulation material for rotating machines based on polymer/MgO

Composite insulation systems are an inseparable part of high voltage equipment. The strongly inhomogeneous structure of these materials is the main problem which may lead to defect during its operation. The main aim of this paper is to describe new composite insulation material with the polymer matrix, magnesium oxid filler and polyethylene naphthalate carrier. Dielectric properties like dissipation factor, dielectric strength and volume resistivity are described in this paper. Measurement of partial discharge (PDs), charge dynamics during voltage -on and voltage -off measurements and broadband dielectric spectroscopy measurement were performed, as well.

Antioxidant variations in the nature ester oil

The insulating liquids for power transformers are still evolving area. The current trend is to move away from currently used mineral oil because it poses a threat to the environment and use the renewable, biodegradable nature ester oils instead. These oils are now well known but what keeps them from widespread usage are unbalanced properties. In some areas these natural oils excel (fire point, sulfur content, etc.) but in others they still need improvement (dissipation factor, oxidative stability). This paper deals primarily with dielectric properties of the nature ester oil (rapeseed oil) with a focus on improvement of an oxidation stability. The emphasis is placed on a conservation of good dielectric properties for a long time thanks to the addition of an antioxidant. The experiment is based on preparation and measurement of the rapeseed oil with the different amount of several antioxidants. Evaluation of the impact of antioxidants on the dielectric properties of oils in the supplied state is performed via measurement of a breakdown voltage and a dissipation factor. The effect of antioxidant addition on the properties of oil, which is exposed to elevated temperature, is determined via a test of oxidation stability. The evaluation of this test is based on the comparison of values of the dissipation factor at the beginning and at the end of the test. The additional method for assessing of changes in the chemical structure (associated with oxidation processes) is Fourier transform infrared spectroscopy.

Dielectric spectroscopy and absorption/resorption analysis of composite dielectric with MgO filler

Composite insulation systems are inseparable part of most electrical installations. Strongly inhomogeneous structure of these systems is the main problem which may lead to defect during operation life. Main aim of this paper is to introduce novel composite material designed for insulating system of high voltage equipment. This material is composed of epoxy resin matrix with dispersed magnesium oxide (MgO) nanoparticles and polyethylene naphthalate (PEN) film. The main emphasize is placed on behaviour of this material in AC electric field depending on frequency of testing voltage and ambient temperature and also on the behaviour in DC field. The characterization in AC field is based on broadband dielectric spectroscopy, on the other hand the behaviour in DC field is characterized by dielectric absorption. Parameters like real permittivity, loss factor and dielectric absorption and resorption are mentioned in this paper.

Investigation of filling level and processing technology influences on dielectric behavior of PE/HNT nanocomposites

This paper provides an overview of the dielectric behavior of composites consisting of polyethylene and halloysite nanotubes. The aim is to evaluate the changes in the dielectric properties depending on the different level of HNT filling and differences in processing technologies. The emphasis is placed on the evaluation of dielectric polarizations and their basic mathematical description. Furthermore, the attention is given to the behavior of electric conductivity. Composites were divided into two groups according to the used processing technologies and were prepared with three different filling levels. The first processing method included a simple kneading and compressing of the mixture and the second method used a small scale extrusion. The real part and the imaginary part of a complex relative permittivity were selected as key variables through the Broadband Dielectric Spectroscopy. Results obtained by measuring over a wide frequency and temperature range were supplemented by a mathematical model of dielectric polarizations according to Havriliak-Negami theory. Moreover, the most probable relaxation times of observed polarizations were calculated for each temperature and the fitting according to Arrhenius theory was performed.

Influence of Halloysite nanotubes in low-density polyethylene on electric polarization

This paper deals with the influence of nanofiller on the behaviour of polymer dielectric in an electrical alternating field. As the basic polymer is selected a linear low-density polyethylene and as a nanofiller a perspective material based on aluminosilicates known as the Halloysite nanotubes is used. A broadband dielectric spectroscopy is applied as a diagnostic method. This method allows us to measure the real and imaginary part of the complex relative permittivity. The effect of different filling of polymer material with nanotubes to the ongoing polarization process is evaluated on the basis of the trend of the permittivity. Besides the influence of the simple presence of nanofiller, the effect of variable temperature is also taken into consideration. The measured data is evaluated as the frequency and temperature dependence with an emphasis on the interconnection of frequency and temperature effects. Subsequently, the data are processed as Cole-Cole diagrams (circular and linearized). These diagrams offer a slightly different view on the solved issue. The paper concludes with a calculation of the relaxation times of the polarization, which were registered in the selected frequency and temperature range. The relaxation times calculation is based on the theory of Cole-Cole diagrams. Linearized Cole-Cole diagram has been designed mainly for the calculation of relaxation times.

Polarization of LLDPE/HNT and HDPE/HNT blends in AC electric field

Halloysite nanotubes (HNT) represent a type of aluminosilicate clay of natural origin with nanotubular structure. HNT have been started to use in many industrial fields, including the application in the electrical engineering. This paper is focused on the determination of dielectric properties of pure halloysite nanotubes, as well as, a polyethylene (LLDPE and HDPE) based HNT nanocomposite (blends). Individual samples in each series had contained different amount of HNT filler. The impact of the HNT content and the impact of the type of polyethylene on the dielectric properties were observed and evaluated. Measurements were carried out under the AC field via a broadband dielectric spectroscopy. Dielectric properties were evaluated through real and imaginary parts of the complex relative permittivity. Results are displayed as surface visualizations of frequency and temperature dependence. The relaxation times of selected relaxation processes were analyzed according to the theory of relaxation polarization.